This invention relates to turbine engine blading members, for example blades, vanes and struts. More particularly, it relates to composite gas turbine engine blades, especially those made of a low ductility material such as a ceramic matrix composite.
Current axial flow turbine engines include a variety of types of blading members, for example axially aft generally from a fan section through a compressor section and though a turbine section. The function of such turbine engine blading members is well known and widely described in the turbine engine art. Of particular interest in connection with a form of the present invention are blades located in the turbine section of a gas turbine engine because of the strenuous, high temperature operating conditions experienced by such component.
Typical axial flow gas turbine engine turbine blades comprise an airfoil having a tip at a radial outer end, a base having a radially inner end and a platform between the airfoil tip and the base radially inner end. Examples of turbine engine turbine blades are described in such U.S. Pat. No. 5,813,188—Roedl et al, and U.S. Pat. No. 6,106,231—Brainch et al.
Current development of turbine section blades, vanes, struts, shrouds, etc. has suggested use of relatively low ductility ceramic base materials, commonly called ceramic matrix composites (CMC), because of their capability of operating at temperatures higher than can metal alloys, even with air cooling. However such materials have mechanical properties that must be considered during design, manufacture and application of an article such as a blading member. For example, CMC type materials have relatively low tensile ductility or low strain to failure when compared with metallic materials. Generally, commercially available CMC materials include a ceramic type fiber for example SiC, forms of which are coated with a compliant material such as BN. The fibers are carried in a ceramic type matrix, one form of which is SiC. Typically, CMC type materials have a room temperature tensile ductility of no greater than about 1%, herein used to define and mean a low tensile ductility material. Generally CMC type materials have a room temperature tensile ductility in the range of about 0.4-0.7%. This is compared with typical high temperature alloys having a room temperature tensile ductility of at least about 5%, for example in the range of about 5-15%. Accordingly because of manufacturing limitations using CMC type low ductility materials, in one example a turbine blade with a CMC airfoil and base has included a platform, typically of metal, as a separate and distinct portion of the blade. In such a configuration, a gap between the separate platform and the balance of the blade has been found to be difficult to seal and has allowed an amount of uncontrolled leakage from the engine flowpath about the airfoil through the gap toward the base. Such uncontrolled leakage can adversely affect engine efficiency. It would be advantageous to provide such a CMC blade with a CMC airfoil, platform and base as an integral article, eliminating a potential gap between the platform and the remainder of the blade.